Removing sulfur bearing compounds from crude oil/refined organic fuels is an extremely important objective. In fact, it is being mandated that sulfur levels need to get to as close to zero as possible. Conventional methodology has been to utilize hydrodesulfurization to remove sulfur atoms from hydrocarbon molecules via the application of hydrogen gas under high heat and pressure to ultimately produce hydrogen sulfide gas, which then may be subsequently converted to elemental sulfur. However, hydrodesulfurization is very costly as a capital expenditure as the necessary equipment is expensive and the process consumes substantial energy, as well as requires the use of catalysts and a source of hydrogen. Moreover, hydrodesulfurization is only partially effective in removing sulfur from hydrocarbons and cannot remove certain types of sulfur material, especially sterically-hindered organic sulfur-bearing compounds such benzothiophene compounds, which include benzothiophene, dibenzothiophenes, napthothiophenes and their mono, di and tri-alkyalted derivatives. Indeed, this family of molecules is the most expensive to remove and requires more severe hydrotreater pressure and heat, as well as hydrogen. Indeed, it is well recognized that benzothiophene compounds are the species that require the real majority of the energy and expense (up to 90%) to remove from hydrocarbon streams.
Oxidative desulfurization, as an alternative to hydrodesulfurization, has been around for a long time as a method to try to address this concern. Exemplary of such processes include those disclosed in U.S. Pat. Nos. 1,972,102 and 3,505,210. Such processes essentially involve oxidizing the organic sulfur-bearing compound to a sulfone or sulfoxide through the use of an oxidizing agent, typically hydrogen peroxide, in an acidic, aqueous environment, and thereafter removing the oxidized sulfur species by a variety of techniques based on the change in the chemical properties due to the oxidation of the sulfur atom.
Although effective, such methodology has not been commercialized because of the reaction time it takes to oxidize the aforementioned secondary sulfur species that are sterically-hindered and not readily accessible to oxidation, especially when an entire stream must be treated, which in some applications is simply too much volume to practically treat and is cost prohibitive. To enhance and expedite the oxidation reaction, attempts have been made to apply other energy sources, such as heat, pressure, microwaves, ultrasound, etc., to enhance or bolster the oxidative reaction. Exemplary of such further advancements in oxidative desulfurization include the disclosures in Applicant's U.S. Pat. No. 7,081,196, entitled TREATMENT OF CRUDE OIL FRACTIONS, FOSSIL FUELS, AND PRODUCTS THEREOF WITH SONIC ENERGY, and U.S. Pat. No. 7,871,512, entitled TREATMENT OF CRUDE OIL FRACTIONS, FOSSIL FUELS, AND PRODUCTS THEREOF, the teachings of which are expressly incorporated herein by reference.
However, these oxidative-based sulfur removal applications can still be costly compared to hydrodesulfurization because the infrastructure to perform hydrodesulfurization is already in place and the results, despite being sub-optimal, are at least known, as well as what the operating costs will be to apply such industrial application. Moreover, while ultrasound-assisted oxidative desulfurization generally works, the cost to apply such technology to treat a whole, entire stream of a refined organic fuel (e.g., diesel), as well as and the cost and risk in using such technology as a new treatment for a whole refinery is daunting from an investment standpoint, and using such a technology to address the problem may not be a practical or cost effective way to remove difficult sulfur species from the refined product on a large scale.
The complications associated with removing sulfur from refined hydrocarbon fuels/fossil fuel fractions are also present in post-refining operations and create a separate need to remove sulfur species despite previous treatment with an initial sulfur removal process. More specifically, refined petroleum products that are transported by pipeline normally are pumped sequentially, as a continuous flow through the pipeline. As a result, some amount of mixing of adjacent product types normally occurs. The product in a pipeline between two adjacent volumes of petroleum product consists of a mixture of the two adjacent volumes and is called “interface.” Generally, interface mixture is blended into the two adjoining products that created the interface. Transmix is an interface consisting of two adjacent dissimilar petroleum products, such as gasoline and distillate fuel, which cannot be blended into either of the two adjacent products without causing either of them to violate commercial standards.
Since the transmix cannot be blended into either of the two adjacent products transported by the pipeline, it is diverted by the pipeline into a separate storage tank. Transmix is generally transported via tank truck, pipeline or barge to a facility designed to separate the transmix into its fuel components. For example, where the transmix consists of gasoline and distillate fuel, the transmix may be transported to a “transmix processing” facility where the gasoline portion is separated from the distillate fuel. At locations where it is either relatively expensive or inconvenient to transport transmix to a transmix processing facility for separation, the transmix is sometimes blended into gasoline in very small amounts, typically around 0.25 volume percent of the gasoline.
Transmix processors and transmix blenders, however, are refiners under the Environmental Protection Agency (EPA) regulations. Historically, the EPA provided transmix processors and transmix blenders with flexibility in complying with refiner requirements. That flexibility, however, is nearly at end, requiring transmix processors and transmix blenders to comply with gasoline sulfur regulations under 40 CFR Part 80, subpart H. As a consequence, an entire, separate, post-refining industry is now faced with the same challenges as refiners, and now must implement measures to reduce the levels of sulfur to levels that comply with regulatory requirements which are becoming increasingly stringent.
Accordingly, there is a need in the art for processes that can facilitate the removal of sulfur from refined hydrocarbon streams, including difficult to remove sulfur species that are commercially practical, efficient and cost effective. There is likewise a need in the art for processes that can facilitate the removal of sulfur from refined hydrocarbon streams that can be readily deployed in existing refining facilities utilizing existing hydrodesulfurization infrastructure, yet need only require treatment of a small fraction of the hydrocarbon stream to remove problematic organic sulfur species. There is still further a need for processes that can facilitate the removal of sulfur from refined hydrocarbon streams that can be utilized in transmix operations to remove problematic organic sulfur species present in post-refined hydrocarbon streams.